Tankpedia is a website about Armoured Fighting Vehicles especially tanks.

During the Second World War, as conflict raged across Europe and the Asian Pacific theatre, local arms production became paramount for Australia. In 1940, design work begin on a native tank design. The result would be the AC I, known as the Sentinel; the only notable tank to be produced in Australia. The goal was to create a Cruiser tank with a 2 pounder gun weighing between 16 and 20 tonnes. A mission was dispatched the the United States to review the M3 “Lee” Medium tank. Colonel W. D. Watson MC, an artillery officer with tank design experience, was provided by the United Kingdom to shepherd the project; arriving in December of 1940. Borrowing from the Canadian Ram tank design, the AC I was to use the engine, drive train, and lower hull of the M3; the upper hull and turret were to be based on the existing British Crusader tank design. By 1942, both the weight and the silhouette for the AC I design had increased in-line with that of U.S Medium tanks; in an effort to keep pace with German Medium tank designs.

The original design was intended to utilize a 2 pounder gun; a QF 2 pounder. As the design progressed a QF 6 pounder was chosen instead for the main armament over the QF 2 pounder. Additionally the design boasted two additional secondary armaments in the form of two Vickers machine guns; one placed in the hull and the other mounted coaxially with the main gun.

In February of 1942 the AC I received the moniker, “Sentinel”. Manufacturing began for the AC I in August of 1942. Manufacturing for the AC I took place in Sydney at the Chullora Tank Assembly Shops by New South Wales Railway Company; where trials for the vehicle also took place.

In the end, 65 vehicles were built by June of 1943. Due to shortages, these tanks used the QF 2 pounder as the QF 6 pounder was not available; further, as a desirable single engine was not available, these vehicles used not one, but three Cadillac 346 in³ (5.7 L) V8 petrol car engines installed in clover-leaf configuration and all three feeding the same gearbox. The AC I possessed a fully cast hull and a fully cast Turret; no other vehicles from this period have a fully cast hull.

While the armaments of the AC I where comparable to a British Cruiser design, the final weight of approximately 28.4 tonnes (comparable to the US M3 at 27.2 tonnes, and the US M4 at 30.3 tonnes), put this vehicle out of this classification. Cruiser tanks are by definition fast tanks; which implies, lightly armed and armoured to encourage speed. Comparing the AC I to two British examples of a Cruiser, the Cruiser Mark 1, and the Cruiser Mark IV tanks:

Tank:

AC I Sentinel

Main Armament:

QF 2 pounder

Weight:

28.4 tonnes

Speed:

48 km/h on-road (ostensibly)

Tank:

Cruiser, Mk I

Main Armament:

QF 2 pounder

Weight:

10.9 tonnes

Speed:

40 km/h on-road (ostensibly)

Tank:

Cruiser, Mk VI, “Crusader”

Main Armament:

QF 2 pounder

Weight:

20 tonnes

Speed:

42 km/h on-road, and 24 km/h off-road

In spite of the Medium tank qualities the AC I possessed (weight and overall silhouette), we can see the final design was a healthy example of a Cruiser. The design reflected Cruiser and Medium tank inspirations, and the ingenuity of the peoples of Australia, to defend their homeland.

“Australian Sentinel Tank.” Australian Military Vehicles Index. Sentinel: A Site Dedicated to the Research and Modeling of Australian Military Vehicles, n.d. Web. 25 July 2016. <http://www.mheaust.com.au/Aust/Research/Sentinel/sentinel13.htm>